This invention relates to flat article singulation mechanisms and to sensors suitable for use therewith. More particularly, this invention relates to a mechanism for controlling the presentation of articles to a singulation head of a flat article singulation system and to sensors suitable for use in such a mechanism, which sensors detect the pressure at which an article is pressed against a surface with high precision and with easy range adjustability.
There are many applications, including the processing of mixed mail, where a need exists to singulate a single flat article from a stack of such articles at relatively high speed and with wide variations in the size, thickness and weight of the articles being singulated, while still maintaining high controllability on the outputted articles, a low jam rate, low damage rate, and substantial elimination of doubles passing through the singulation mechanism. While many mechanisms exist for reducing the incidence of doubles passing from a singulation head to a takeaway mechanism, no such mechanism can be completely affective in catching and eliminating all doubles which occur, a doubles being defined as an article which sticks to an article being singulated and passes to the takeaway mechanism with such article. It is therefore desirable to design the singulation mechanism so as to minimize the incidence of doubles, and thus the number of doubles which must subsequently be resolved. However, while it has been generally understood that the occurrence of doubles can be reduced by controlling the presentation of the articles to the singulation head, there has been little understanding of exactly how to control such presentation so as to minimize doubles. Further, in order to control presentation of flat articles to the surface of the singulation head, it is necessary to accurately sense the pressure at which articles are being pressed against the head, preferably over a fairly wide pressure range. Suitable pressure sensors for such application have not heretofore existed.
In accordance with the above, it has been found that two factors in the presentation of flat articles, such as mixed mail, to a singulation head influence the incidence of doubles, these factors being the pressure at which the stack of articles is pressed against the head and the angle of the stack relative to the head. In particular, for a given singulation mechanism operating under selected specifications as to size, thickness and weight of the flat articles to be singulated, there will be a particular target pressure which is optimum for singulation without the incidence of doubles, and there will be a pick window of pressures around such target pressure at which singulation can be successfully performed. The further the instantaneous pressure of the lead article in the stack, the article to be singulated, against the singulation head deviates from the target pressure, the more likely it is that doubles will occur. When the pressure is outside of the pick window, successful singulation can no longer be assured. Similarly, there is an optimum angle of presentation for the articles in order to achieve doubles free singulation, and there is a range of angles of presentation for articles beyond which successful singulation can not be assured. A successful singulation mechanism should therefore be designed so as to only be operable when the pressure at which articles are being pressed against the singulation head is within the pick window and when the angle of presentation is within a range at which successful singulation can be achieved. The singulation mechanism should also be designed to maintain the presentation pressure for the articles being singulated as close to the optimum target pressure as possible and to maintain the angle of presentation as close to a desired target angle as possible.
The invention thus provides a mechanism for controlling the presentation of articles to the singulation head of a system for singulating a stack of edge-mounted articles, which mechanism includes at least one servo-controlled drive member for moving the stack of articles toward the head, with a leading article of the stack, which article is to be singulated, contacting the head at an instantaneous pressure; a sensor mounted in the head for detecting such instantaneous pressure; and a feedback control operative in response to the difference between the detected instantaneous pressure and a target pressure for controlling the drive member so as to reduce such difference. For a preferred embodiment, such sensor is mounted in a lower portion of the head, and a second pressure sensor is also provided which is mounted in an upper portion of the head, the feedback control operating on the drive member in response to instantaneous outputs from at least the second pressure sensor, and generally from both pressure sensors, to control orientation of the stack of articles relative to the front face of the head. For a singulation head having a drive belt which picks off the leading article, the sensor and second sensor may be below and above the belt, respectively.
A second component may be provided for applying a controlled bias pressure to at least one of the sensors, such component being a servo motor for preferred embodiments, the bias pressure applied by the servo motor being determined by a control signal applied thereto. A separate servo motor is preferably provided for controlling bias pressure for each sensor. A separate position encoder may also be provided for each sensor, the position encoder preferably being a precision encoder which detects movement of a lever which moves in response to pressure applied thereto in the 10xe2x88x923 range.
For a preferred embodiment, there are two servo-controlled drive members, a servo-driven belt on which an edge of each article rides and a servo-driven pusher on a back of the stack. The belt may for example respond primarily to an output from the sensor to control stack pressure against the head and may also be used to control orientation; the pusher may respond to both sensors to control orientation of the stack relative to the face of the head and to also control pressure. For some embodiments, the feedback control is operative to control the drive member at a rate which is related to the difference between instantaneous pressure and target pressure. For preferred embodiments, there is also a pick window of instantaneous pressures at which singulation can effectively be performed by the head, and a control is provided which inhibits operation of the head when the instantaneous pressure sensed by the sensor, or at least by the lower sensor where two sensors are employed, is outside of such pick window. The control inhibiting operation of the singulation head may also be operative where the angle of presentation is detected as being outside of an acceptable range.
The invention also includes a sensor for detecting the pressure at which an article is pressed against a surface, which sensor includes a lever extending from such surface, the lever being moved a selected distance in a selected direction in response to an article being pressed against the surface at pressures within a selected range, and a servo motor connected to the lever to apply a bias pressure thereto in a direction opposite the direction of lever movement under pressure from the article, the bias pressure being determined by a control signal applied to the motor. The sensor also includes, for preferred embodiments, a position encoder generating an output indicative of lever position in the selected direction. The position encoder is preferably a precision encoder capable of detecting movements of the lever in the 10xe2x88x923 inch range.
Finally, the invention includes a method for controlling the presentation of articles to the singulation head of a system for singulating a stack of edge-mounted articles, the method including using a sensor mounted in the head to detect the instantaneous pressure at which a leading article in the stack, which article is to be singulated, is pressed against the head; determining the difference between each instantaneous pressure and a target pressure; and utilizing such difference to control at least one drive mechanism moving a stack of articles substantially perpendicular to a singulation face of the head in a manner so as to reduce such difference. There is preferably a pick window for the instantaneous pressure, the method including inhibiting operation of the singulation head during any period when the instantaneous pressure detected is outside of such pick window. A similar inhibiting operation may occur when the presentation angle of articles is outside of an acceptable range. For a preferred embodiment, there are two sensors, a first sensor mounted in a lower portion of the head and a second sensor mounted in an upper portion of the head, and there are two drive mechanisms, a first drive mechanism on which the edges of the articles ride and a second drive mechanism pushing on the back of the stack, the method for such embodiment including the steps of controlling at least the first drive mechanism in response to the difference detected at least by the first sensor to reduce such a difference; and controlling at least the second drive mechanism in response to pressure detected by both of the sensors to control orientation of the stack relative to the head and preferable to also control pressure. The drive mechanism may be controlled at a rate which is related to the difference between instantaneous and target pressure.
The foregoing in other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings. Like reference numerals are used to refer to common elements in the various drawings.